Partially esterified regenerated cellulose film as a packaging material



United States Patent 3,311,498 PARTIALLY ESTERIFIED REGENERATED CELLU- LOSE FILM AS A PACKAGING MATERIAL John T. Massengale, West Chester, and Edward A. Wielicki, Philadelphia, Pa, assignors, by mesne assignments, to FMC Corporation, San Jose, Calif a corporation of Delaware No Drawing. Filed May 21, 1963, Ser. No. 282,151 9 Claims. (Cl. 117-145) This invention relates to a packaging material of dimensionally stable, partially esterified, regenerated cellulose film.

Non-fibrous regenerated cellulose sheets have been extensively used as packaging material. However, these sheets and films are subject to expansion and contraction with changes in relative humidity, causing surface wrinkles or cockling. This is not only unsatisfactory from the standpoint of appearance, but these dimensional changes may cause actual rupture of the film and minute breaks in any coating thereon, thus reducing the protective value of the sheet or film.

Regenerated cellulose films, in order to have heat-sealing and moisture-resistant properties, must be coated with a layer of another film-forming material having such properties. The base film requires treatment with an anchoring agent to provide the necessary adhesion for the coating material. However, the anchorage of the coating to the film may have limited life, depending on the environment of the coated film. Once the coating becomes detached from the base film, the effectiveness of the film as a protective overwrap is lost.

In addition to the above film packaging problems, most films which are presently used as packaging materials including tapes, labels and sheets, have limited utility from the standpoint of heat resistance. These films, when subjected to high temperatures (above 180 C.), either decompose or soften. The few films available which are relatively heat-resistant are too expensive for general use.

Therefore, it is a principal object of this invention to provide a relatively inexpensive heatand water-resistant, dimensionally stable packaging film.

It is another object of this invention to provide a composite sheet for packaging having improved heat and water resistance, dimensional stability and heat-sealability.

It is still another object of this invention to provide an improved package including an outer packaging material, e.g., tape, label or wrapping which is highly resistant to heat and moisture, and remains dimensionally stable when subjected to these conditions.

It is a further object of this invention to provide a 'cellulosic packaging film having improved properties for the reception and adherence of coatings and inks.

These and other objects are accomplished in accordance with this invention which comprises a heatand waterresistant, dimensionally stable packaging material of a partially esterified, non-fibrous regenerated cellulose sheet. The packaging material of this invention is a regenerated cellulose sheet which has been processed in a controlled acetylating procedure whereby the sheet remains intact but the cellulose is partially derivatized to produce the additional desirable packaging properties. Partial esterification in this case may be broadly defined as a cellulose sheet material having an average degree of substitution of between about 0.2 and 2.8 ester groups per anhydroglucose unit of the cellulose molecule.

This invention is preferentially concerned with thin (about 1 mil and less), clear regenerated cellulose films which may be in the form of tapes, labels or wrapping sheets. The films, after acetylation, may be coated with compositions containing film-forming resins to further 3,311,498 Patented Mar. 28, 1967 "ice modify the film properties, e.g., heat-sealing. Examples of film-forming coating materials include nitrocellulose, vinylidene halide copolymers, vinyl halide copolymers, polyolefins, acrylic polymers and copolymers, etc. These coating compositions may be applied to the base sheet by organic solvent, aqueous dispersion or melt extrusion techniques.

The films permit package outerwraps substantially free from wrinkles and breakage even when subjected to severe changes in humidity.

The packages of this invention include food stuff, wearing apparel and other articles of manufacture which may or may not be enclosed in other containers for example, cartons, wrapping sheets, boxes, jars and bottles. These packages are overwrapped, i.e., taped, labeled, or completely enveloped, with the partially acetylated film of this invention. Labels of this material are very useful since they are water-resistant, print well, are clear, glossy and durable.

While the acetylating procedure which is used to obtain the modified films of this invention may be any method which will produce a wrapping material having the abovedescribed properties, the preferred procedure is as follows.

Wet gel or re-wet unplasticized regenerated cellulose film, preferably 1 mil thick or less, is run through one or more activation baths, consisting of glacial acetic acid at room temperature. From the activation bath the film is run through one or more catalyst baths and then advanced through an acetylating bath or baths. The film is then run through a catalyst inactivation bath, water wash baths, plasticization baths and dried. Films produced in the above and equivalent methods have a range of acetyl content not otherwise obtainable. In addition such films can be produced at much higher speeds and more economically than solvent cast conventional acetate films and removal of the casting solvent is not required.

An example of the production of a film of this invention is as follows.

Example A wet gel, unplasticized regenerated cellulose film from a production line, having a dry thickness of 0.9 mil, is run through a series of baths at a speed of about ft./ min. The bath composition, temperature and number of baths per treatment in consecutive order is given below.

1 Plasticizer.

The product film has an acetyl content on the cellulose of 35% and about 13% plasticizer based on the weight of the film.

In acetylation processes as above-described other catalysts may be used in place of the preferred perchloric acid. Sulfuric acid, phosphoric acid, trifluoroacetic acid, boron trifiuoride, etc., are examples of such catalysts.

In place of the acetylation of regenerated cellulose films, one may partially esterify the preformed film with other lower fatty acid anhydrides, e.g., propionic or butyric anhydride.

As previously stated, the films of this invention have unexpectedly high heat resistance. The test films were heat stable at 200 C. while conventional cellulose acetate and triacetate films containing nominal amounts of plasticizer softened.

The insensitivity of the film heat and solvents permits easy coating of the film without softening, distorting, and stretching. Conventional cellulose acetate, either secondary or triacetate, would be softened at efiicient operating conditions. Solvent removal after coating is made easier.

The ability to readily coat the film of this invention means that a high moisture barrier product can be made. This is of significance for overwrapping, since one of the major areas of merit is that this film has low moisture expansivity, about the same as that of carton paperboard. Equal expansivity of overwrap film and cartons and high barrier value of the overwrap film are two major sought after characteristics.

Resistance to heat permits one to use a heat-sealing coating. The coatings can be joined for two pieces of film without distorting the base film.

Test films of this invention were coated with a 90% vinylidene chloride acrylonitrile copolyrner lacquer. The anchorage was evaluated by the boiling water method. A control was run for the test procedure using conventionally anchored raw stock regenerated cellulose film coated with the same lacquer. The boiling water anchorage test result on the coated, partially acetylated film was 244 seconds while the control took 36 seconds for the coating to loosen.

Various changes and modifications may be made practicing the invention without departing from the spirit and scope thereof and, therefore, the invention is not to be limited except as defined in the appended claims.

We claim:

1. A heatand water-resistant dimensionally stable film prepared by partially esterifying a non-fibrous regenerated cellulose film.

2. The film of claim 1 which has been partially esterified to an average degree of substitution of between 0.2 and 2.8 acetyl groups per anhydroglucose unit of the cellulose molecule.

3. The film of claim 1 having a heat-scalable coating on at least one side thereof.

4. A package having an outer wrapping of a heatand water-resistant dimensionally stable film, said film prepared by the partial esterification of a non-fibrous regenerated cellulose film.

5. The package of claim 4 wherein the regenerated cellulose film is partially esterified to an average degree of substitution of between about 0.2 and 2.8 acetyl groups per anhydroglucose unit of the cellulose molecule.

6. The package of claim 4 wherein the outer wrapping is a label.

7. The package of claim 4 wherein the outer wrapping is a tape.

8. The package of claim 4 wherein the dimensionally stable film is coated on at least one side thereof with a heat-scalable coating.

9. The package of claim 8 wherein the heat-scalable coating is a resinous interpolymer of a major proportion of vinylidene chloride.

References Cited by the Examiner UNITED STATES PATENTS 2,770,555 11/1956 Cornwell 117-444 2,900,669 8/1959 Booth 106196 2,986,270 5/1961 Harwood 206-46 2,993,749 7/1961 Sloan et al. l06-196 3,019,119 1/1962 Hoffman et al. l06-196 3,039,986 6/1962 Blood et al. 1l7144 3,057,755 10/1962 Malrn et al. l17-l44 ALFRED L. LEAVITT, Primary Examiner.

A. H. ROSENSTEIN, Assistant Examiner. 

4. A PACKAGE HAVING AN OUTER WRAPPING OF A HEAT-AND WATER-RESISTANT DIMENSIONALLY STABLE FILM, SAID FILM PREPARED BY THE PARTIAL ESTERIFICATION OF A NON-FIBROUS REGENERATED CELLULOSE FILM. 